Both hyperthermia treatment and certain chemotherapy drugs have been shown to be more effective if treatment is conducted at low pH (6.7 - 7.0). Should tumors possess regions of low pH due to nutrient depletion and compromised circulation, these findings would have clinical implications. While several laboratories and clinics have measured the pH in small tumors, data regarding large tumors is lacking. Using a specially designed fiber optic pH probe, tumor pH at various sites will be determined for large pancreatic tumors. Pathology at the site of pH measurement will also be determined. These data will be compared to the pH of normal tissue.